Sat Sep 8, 2012, 09:44 AM
n2doc (41,531 posts)
Uncertainty over Heisenberg’s ‘Uncertainty Principle’
Since 1927, when Werner Heisenberg formulated the uncertainty principle, it has stood as one of the cornerstones of quantum mechanics. In a simplified form, the uncertainty principle states that it is impossible to measure anything without disturbing it. For example, any attempt to measure a particle’s position must randomly change its speed.
For clarity’s sake, one should be aware that the uncertainty principle is not the same as the observer effect, which states that the act of observing a phenomenon will change the phenomenon itself. The uncertainty principle is more about how precisely something can be measured in two dimensions such as position and momentum, simultaneously. In common parlance, the two theories are often conflated. This principle has driven quantum physicists crazy for nearly a century. That is, it drove them crazy until recently, when researchers at the University of Toronto demonstrated the ability to directly measure the disturbance and confirm that Heisenberg was too pessimistic. “We designed an apparatus to measure a property – the polarization – of a single photon. We then needed to measure how much that apparatus disturbed that photon,” says Lee Rozema, a Ph.D. candidate in Professor Aephraim Steinberg’s quantum optics research group at U of T. more http://www.redorbit.com/news/science/1112689943/heisenberguncertaintyprinciple090812/

9 replies, 2930 views
9 replies  Author  Time  Post 
Uncertainty over Heisenberg’s ‘Uncertainty Principle’ (Original post) 
n2doc  Sep 2012  OP 
leveymg  Sep 2012  #1  
2on2u  Sep 2012  #2  
Jim__  Sep 2012  #3  
bananas  Sep 2012  #5  
bananas  Sep 2012  #6  
Fantastic Anarchist  Apr 2013  #9  
pokerfan  Sep 2012  #4  
Tony Fleming  Apr 2013  #7  
hrmjustin  Apr 2013  #8 
Response to n2doc (Original post)
Sat Sep 8, 2012, 09:48 AM
leveymg (34,080 posts)
1. It remains a great metaphor for journalism, anthropology, and all observation of human activity
Nietzsche may have captured it:
"Look not into the abyss, lest the abyss look into thee." 
Response to n2doc (Original post)
Sat Sep 8, 2012, 10:45 AM
2on2u (1,843 posts)
2. This stuff makes my head hurt and not a little bit, but rather a whole lot. n/t
Response to n2doc (Original post)
Sat Sep 8, 2012, 11:00 AM
Jim__ (10,019 posts)
3. Does this mean that the limit that Heisenberg put on the precision of the measurement is wrong?
Or, does it imply that Heisenberg's "Uncertainty Principle" is intrinsically wrong and that there is not necessarily any limit on how precisely something can be measured in 2 dimensions?

Response to Jim__ (Reply #3)
Sat Sep 8, 2012, 04:12 PM
bananas (26,689 posts)
5. Depends which Heisenberg limit you're talking about.
http://physics.aps.org/synopsisfor/10.1103/PhysRevLett.109.100404
While the measurements by Rozema et al. leave untouched Heisenberg‘s principle regarding inherent quantum uncertainty, they expose the pitfalls of its application to measurements’ precision. http://arxiv.org/abs/1208.0034
While there is a rigorously proven relationship about uncertainties intrinsic to any quantum system, often referred to as "Heisenberg's Uncertainty Principle," Heisenberg originally formulated his ideas in terms of a relationship between the precision of a measurement and the disturbance it must create. Although this latter relationship is not rigorously proven, it is commonly believed (and taught) as an aspect of the broader uncertainty principle. 
Response to Jim__ (Reply #3)
Sat Sep 8, 2012, 04:39 PM
bananas (26,689 posts)
6. weak measurement
http://blogs.scientificamerican.com/observations/2011/09/21/quantumcheshirecatevenweirderthanschrodingers/
Quantum Cheshire Cat: Even Weirder Than Schrödinger’s By George Musser  September 21, 2011 <snip> The situation is an elaboration of Schrödinger’s thought experiment. You have a cat. It is either purring or meowing. It is curled up in one of two boxes. As in Schrödinger’s scenario, you couple the cat to some quantum system, like a radioactive atom, to make its condition ambiguous—a superposition of all possibilities—until you examine one of the boxes. If you reach into box 2, you feel the cat. If you listen to the boxes, you hear purring. But when you listen more closely, you notice that the purring is coming from box 1. The cat is in one box, the purring in the other. Like a Cheshire Cat, the animal has become separated from the properties that constitute a cat. What a cat does and what a cat is no longer coincide. In practice, you’d pull this stunt on an electron rather than a cat. You’d find the electron in one box, its spin in the other. Even by the standards of quantum mechanics, this is surprising. It requires what quantum physicists call “weak measurement,” whereby you interact with a system so gently that you avoid collapsing it from a quantum state to a classical one. On the face of it, such an interaction scarcely qualifies as a measurement; any results get lost in the noise of Heisenberg’s Uncertainty Principle. What Aharonov realized is that, if you sift through the results, you can find patterns buried within them. In practice, this means repeating the experiment on a large number of electrons (or cats) and then applying a filter or “postselection.” Only a few particles will pass through this filter, and among them, the result of the softly softly measurement will stand out. Because you avoid collapsing the quantum state, quintessentially quantum phenomena such as wave interference still occur. So, for a Cheshire Cat, you apply the following filter: you change the sign of one term in the superposition, causing the location and spin of the electron to interfere constructively in one box and destructively in the other, zeroing out the probability of finding the electron in box 1 and zeroing out the net spin of the electron in box 2. Voilà, the electron is in box 2 and its spin in box 1. <snip> 
Response to Jim__ (Reply #3)
Wed Apr 24, 2013, 09:06 PM
Fantastic Anarchist (6,071 posts)
9. I'm uncertain of the answer. nt
Response to n2doc (Original post)
Sat Sep 8, 2012, 12:24 PM
pokerfan (27,096 posts)
4. Engage Heisenberg compensators!
When asked "How does the Heisenberg compensator work?" Star Trek technical adviser Michael Okuda responded: "It works very well, thank you."

Response to n2doc (Original post)
Mon Apr 22, 2013, 04:36 PM
Tony Fleming (1 post)
7. HUP 'correct' as engineering approximation but incomplete
It may come as a surprise to past and present adherents of Heisenberg's Uncertainty Principle (HUP) but recent mathematical progress means we can also look at uncertainty from a theoretical point of view. Quantum theory, depending on HUP, is incomplete as Einstein thought. See book Selffield theory, a new mathematical description of physics, by A.H.J. Fleming, published by PanStanford Press 2012; analytic solutions for the motions of the electron and the proton inside the hydrogen atom have been found obviating the need of the numerical and probabilistic quantum theory. The basis of this new formulation includes the magnetic currents of particles and not just the electric fields as in quantum theory. In this formulation, the photon is composite and hydrogeniclike.
It is well known the inequality relationship of HUP applies to any quantum system in general. The equations for the orbital and cyclotron motions of each electron in selffield theory (SFT) are given as two equality equations. Apart from the 'greater than' relationship compared with the exact relationship, the 3 equations are identical. Whereas there is one inexact relationship in HUP there are two equality relationships in SFT. SFT thus completes the Bohr Theory that did not include any magnetic effect on the electron. In the light of this mathematics HUP can be seen as a theoretical error; in practice it appears as a numerical error in any computer calculations. Let me add that HUP will always be a good engineering approximation able to be used across domains from photon to universe in the same way that Newton's law of gravitation is still used today by those involved in gravitational research. Let me further add that the magnetic moments involved in this new mathematics (SFT) at the terrestrial domain may be able to give us much more quantitative information about the way techtonic plates, earthquakes and tsunamis develop over time. But there are other benefits like 'clean' chemistry waiting to be investigated. 
Response to Tony Fleming (Reply #7)
Mon Apr 22, 2013, 05:00 PM
hrmjustin (64,963 posts)